Boost cut off at pressure

[po914]

Hi, i'm new here. Would like to ask for help with my 1989 Euro 930 turbo. The car is 100% stock, so factory turbo, wastegate,...

When i drive the car slowly (no boost) there is no problem. But when i floor the pedal and go above 4000rmp the car hesitates, hiccups. Feels just like all the power is gone.
Verry strange and brutal feeling. There is no problem in 1st and second gear, then i can rev it up at full boost untill the redline.

What could it be? Have read some other treats but i want to be sure before i order new parts.
- Bad fuel pump or filter ?
- Wastegate/intercooler piping broken?
- Wastegate spring or diaphragma?
- Spark plug wiring?
- Boost cut off switch?
- Overboost switch or relais?

Thanks for your help !
Greetings from Belgium

Cedric

[flightlead404]

Could be a boost leak. I had a similar problem with one of the seals on the turbo charge pipe. It was blowing out when I hit boost.

[gsxrken]

Could be any of those things you listed. The only parts I’d order before running all sorts of diagnostics would be a fuel filter, cap, rotor, and properly gapped spark plugs. Those are cheap and never really a waste to do. After that you‘ll need to start troubleshooting- parts are too expensive to spray and pray with.

PS- Do you have a boost gauge or wideband AFR meter? Two relatively minor expenses that might save you thousands and help diagnose your issue as well.

[908/930]

Try bypassing the over boost switch, do not leave it bypassed if that is the problem. Possibly check your ignition timing, make sure distributer is working properly.

[fabregas]

Check the recirculation piston (BOV) in the intake if it’s stuck open.

[1Bad86]

Welcome, It's odd that you can run it up in 1st and 2nd without issues but not 3rd or 4th. Can you do back to back runs in 1st and 2nd without issues? This will help rule out a few things. Forum rules state that you must post a picture of your car for further assistance

[po914]

Originally Posted by 1Bad86

Welcome, It's odd that you can run it up in 1st and 2nd without issues but not 3rd or 4th. Can you do back to back runs in 1st and 2nd without issues? This will help rule out a few things. Forum rules state that you must post a picture of your car for further assistance

I can go in to 1st and 2nd at full boost. 3-4-5 it starts to hesitate at boost rmps...
On small roads where i use only 2nd or so, i can do it for the whole day without any problems.

[po914]

Here is my car. 1989 Slate grey. 3th owner. German Car.

[mark houghton]

Originally Posted by 908/930

Try bypassing the over boost switch, do not leave it bypassed if that is the problem. Possibly check your ignition timing, make sure distributer is working properly.

Based on the description of the symptom being "brutal" complete shutdown, I would surmise the same. Cedric, in order to bypass the over boost switch, you'll need to unplug the wire from it and ground that wire somewhere to the engine. Otherwise the engine (fuel pumps) will not run at all. If that solves the problem you'll have found the culprit. If not, look elsewhere as others have suggested.

[T77911S]

check the rubber elbow from the AFM to the turbo.
if it is soft it WILL collapse.
1st and 2nd are so quick it does not have time to collapse. 3rd and 4th are longer pulls.
eventually it will do it in 1 and 2.

they were only about $50

[po914]

Originally Posted by T77911S

check the rubber elbow from the AFM to the turbo.
if it is soft it WILL collapse.
1st and 2nd are so quick it does not have time to collapse. 3rd and 4th are longer pulls.
eventually it will do it in 1 and 2.

they were only about $50

What is AFM ?

[1Bad86]

AFM - Air Flow Meter, your air box attaches to the top of it. Your looking for the black rubber boot on the left rear of the engine, It kind of looks like a big piece of macaroni. I'd be surprised if that's the issue though as it's pretty stout.

[tops911]

I had an issue like that, ended up the boost was blowing out the spark. Changed the plugs and life was good.

[sunlion]

I have the exact problem in my '84...on cam, on boost, 3rd gear, hard pull.....sputter, then it recovers but by then, I got smoked by a Tesla. Shameful. Already changed plugs, cap and rotor, boost cut off switch, checked timing etc. Happens only on a hard pull, 2nd or 3rd gear. Haven't checked the rubber elbow. Will do that. Drove 200 miles yesterday, happened once on freeway on ramp once it started to pull hard. Happened again later again later in the day racing a tesla...fuel level was very low. Wonder if that had something to do with it.

[gsxrken]

I posted the same thing about a month ago, minus the Tesla humiliation. I still don’t know what it is but it will have to wait a few months now until the NY winter ends and the salted roads are washed away by Spring rainfall.
I tried a new coil (you could too, good spare item to have in the bonnet) but it wasn’t the problem. I’ve wondered about the CDI box, but i think they work or they don’t work. Mine was preemptively renewed by Bob Ashlock a few years back so I’d like to think it’s not suspect but WTF knows.

Originally Posted by gsxrken

My engine is coughing /burping as I wind out a gear under boost. I get off the gas the moment it happens- when it does I see my AFR flash like 17 or 18 momentarily when it bucks.
I know enough that this is usually a boost leak but my TK longneck is well clamped and the only remaining o ring is a brand new Porsche one. My intake blocks are aluminum and fully torqued. New Bosch cap rotor and wpd0 spark plugs. Fuel pressures perfect and AFRs are great until it chops up under hard boost. Brand new injectors. Magnecor wires don’t arc when observed in darkness. I have confirmed that my wastegate opens with metered air pressure from a compressor at the hose that connects to the IC for boost signal. I even ran with my overboost switch wire grounded out to see if I was getting early overboost fuel pump dropout. Nope. What pisses me is that the Coil tests out in spec - .5 between small posts, 675 from either post to center, but think i have ruled everything else out. ? PS- it will wind out and hold 6,000+ if I don’t boost to it. Driveability before the issue is fine

[TDH888]

Originally Posted by po914

Hi, i'm new here. Would like to ask for help with my 1989 Euro 930 turbo. The car is 100% stock, so factory turbo, wastegate,...

When i drive the car slowly (no boost) there is no problem. But when i floor the pedal and go above 4000rmp the car hesitates, hiccups. Feels just like all the power is gone.
Verry strange and brutal feeling. There is no problem in 1st and second gear, then i can rev it up at full boost untill the redline.

What could it be? Have read some other treats but i want to be sure before i order new parts.
- Bad fuel pump or filter ?
- Wastegate/intercooler piping broken?
- Wastegate spring or diaphragma?
- Spark plug wiring?
- Boost cut off switch?
- Overboost switch or relais?

Thanks for your help !
Greetings from Belgium

Cedric

Cedric were you able to solve the problem of your car I’m having this problem as well .

[TDH888]

Originally Posted by T77911S

check the rubber elbow from the AFM to the turbo.
if it is soft it WILL collapse.
1st and 2nd are so quick it does not have time to collapse. 3rd and 4th are longer pulls.
eventually it will do it in 1 and 2.

they were only about $50

Is this the rubber elbow that you replaced . The one encircled w/ a red marker ? Mine is swollen and is soft to squeeze .

[smurfbus]

Thats the one. I had to replace mine too.

[TDH888]

Hi Smurfbus did you have the same problem in your 930 and when you replaced this elbow hose connector the problem was solved ?

[totle]

Sounds like my issue, and it was the overboost switch.
Remove the connector and connect it to ground and go for a ride and see if the cutof goes away